Male infertility is a concern for many couples. Worldwide studies have shown that 2%-7% of all couples have experienced difficulty in achieving conception or are unable to bear children, especially as they near the end of their reproductive life. (Sara A., Advances in Fertility and Sterility, Proc. Twelfth World Congress Fer. Steril. 4:91-92 (1987)). Furthermore, among men who seek help or advice at fertility clinics, slightly more than 10% are diagnosed as having oligospermia or azoospermia of unknown origin. (Hargreave, T. B., The Management of Male Infertility, T. B. Hargreave and T. E. Soon, eds. (Singapore: PG Publishing, pp. 2-21, 1990)). At this time, little is known about the causes of reduced spermatogenesis and, although various treatments are available, improved methods are still needed.